1. Field of The Invention
The present invention relates to the field of anatomical dental restorative systems. More particularly, the present invention relates to the field of impression copings for single-tooth prosthodontics restoration systems.
2. Description of The Prior Art
Anatomical dental restorative systems are commonly used today in single-tooth prosthodontics restorations. Generally, a single-tooth prosthodontics restoration involves the following procedures. First, a dental fixture is implanted into a patient's jawbone. The implant fixture typically has a hole with screw threads for receiving a screw bolt. The exposed end of the implant fixture typically further has a hexagonal interface for defining the orientation of the attachment of a tooth analogue. An impression coping is then attached to the implant fixture to make an impression for transferring to a working cast the natural dentition as well as both the exact position and the exact rotational alignment of the hexagonal interface of the implant fixture. Once the impression is made, it is removed from the patient's oral cavity in the patient's mouth and the impression coping is also removed. The impression coping is then attached to an analogue of the implant fixture and inserted back into the impression, and dental stone or die material is poured in to make the working cast for constructing the tooth analogue. The tooth analogue is finally attached to the implant fixture by a dental abutment.
To obtain the best fitting tooth analogue, it is critical to duplicate both the accurate position of the implant fixture and the rotational alignment of the hexagonal interface of the implant fixture. Therefore, it is very important to prevent both the relative rotation between the impression coping and the implant fixture and the relative rotation between the impression and the impression coping when the impression is made. In order to do so, the impression coping often has a complementary hexagonal interface for establishing non-rotatable engagement with the hexagonal interface of the implant fixture. In addition, the impression coping often has flat exterior surfaces for establishing non-rotatable engagement with the impression.
U.S. Pat. No. 4,955,811 issued to Lazzara et al. on Sep. 11, 1990 for "Non-Rotational Single Tooth-Prosthodontics Restoration" (hereafter the "Lazzara Patent") has disclosed a two-part impression coping, including a coping part and a bolt part. The coping part has a generally cone-shaped body with a narrow top end and a widened bottom end, where the widened bottom end has a male hexagonal interface for fitting snugly with the female hexagonal interface of the implant fixture. The exterior surface of the coping part has a flattened side to restrain the rotation of the impression.
The coping part of the Lazzara Patent further comprises a smooth bore extending through its body from the top end to the bottom end. The entirely smooth bore accommodates the bolt part. The bolt part has screw threads which match the screw threads in the hole of the implant fixture. Once the coping part is placed on the implant fixture and the hexagonal interfaces of the coping part and the implant fixture are properly engaged, the bolt part is extended through the smooth bore of the coping part and threaded into the implant fixture to secure the coping part onto the implant fixture for making the impression.
A problem experienced by dental practitioners which is associated with the Lazzara Patent two-piece type of design of the impression coping, is that the coping part and the bolt part are completely separated and unattachable. The separation and unattachableness of the coping part and the bolt part create several disadvantages. For example, it increases the possibility of mismatching the coping parts and the bolt parts of the impression copings which have different dimensions and specifications. In addition, since the bolt part is introduced into a patient's oral cavity after the coping part is seated on the implant fixture, it increases the difficulty of handling the bolt part and aligning it with the central bore of the coping part. Moreover, it increases the possibility of losing the bolt part in the patient's oral cavity.
Therefore, it is desirable to have an improved type of two-piece impression coping which utilizes a pair of separable but also interlockable coping and bolt pieces to overcome the above identified disadvantages.